Conventionally, in an internal combustion engine in which a plurality of exhaust valves are provided for each of a plurality of cylinders and an exhaust passage is connected to each plurality of exhaust valves, there is proposed a control for those plurality of exhaust valves. For example, in Patent Reference-1, there is disclosed a technique of opening a first exhaust valve in a second half of the exhaust stroke and opening a second exhaust valve in a first half of the exhaust stroke in an engine which includes, for each of cylinders, the first exhaust valve for opening and closing the exhaust passage passing through a turbine and the second exhaust valve for opening and closing the exhaust passage not passing through the turbine. Also, in Patent Reference-2, there is disclosed a technique of stopping one of the valves in each cylinder by using an electromagnetic driving valve, i.e., performing one-side valve stopping drive of the exhaust valve, in order to achieve early activation of the catalyst.
However, in the techniques disclosed in the Patent Reference-1 and Reference-2, there is no disclosure for the catalyst control in an internal combustion engine performing lean burn (i.e., the control for recovering the catalyst purifying performance). Also, in the techniques disclosed in the Patent Reference-1 and Reference-2, there is not disclosed a control method for a system which includes an exhaust gas purifying catalyst provided on the exhaust passages connected to each plurality of exhaust valves and an exhaust gas purifying catalyst provided on the exhaust passage after the junction of those exhaust passages.
Patent Reference-1: Japanese Patent Application Laid-open under No. H10-89106
Patent Reference-2: Japanese Patent Application Laid-open under No. 2000-73790